Microsoft co-founder Paul Allen has made the latest step, unveiling plans for a new commercial spaceship that, instead of blasting off from a launch pad, would be carried high into the atmosphere by the widest plane ever built before it fires its rockets.

He joins Silicon Valley powerhouses Elon Musk of PayPal and Jeff Bezos of Amazon in a new private space race that attempts to fill the gap left when the US government ended the space shuttle programme.

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